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WASHINGTON, D.C.—Last month, the U.S. Fish and Wildlife Commission banned the import of 201 species of salamander into the United States, and between state boundaries. The move is intended to keep out the deadly fungus Batrachochytrium salamandrivorans, or Bsal, sister species of the Bd fungus that has caused the extinction or decline of countless amphibian species. Today, at the annual meeting of AAAS (which publishes Science) in Washington, D.C., four amphibian biologists talked about what they learned from 20 years of the fight against Bd—and why restricting the salamander pet trade was the best way to keep history from repeating itself.
How far has Bsal spread so far?
Bsal was described only about 2 years ago, after it wiped out the fire salamander population in the Netherlands. It has since also been detected in Germany. Its likely origins are in Asia—researchers found the fungus in Chinese museum specimens that are up to 150 years old—and it was probably spread to Europe by the pet trade. “What’s changed is the rate at which we’re moving pathogens around the world,“ Vance Vredenburg, an ecologist at San Francisco State University in California, told the meeting. Because salamanders in Europe have not evolved along with the disease, they are much more vulnerable to it than their Asian relatives. And ever since the fungus was discovered in Europe, researchers have worried that the United States might be its next stop.
What’s the danger?
Bsal causes chytridiomycosis, a disease that eats away at the skin of amphibians. The other known chytridiomycosis-causing fungus, Bd, has already caused amphibian declines and extinctions across the globe—and those declines ripple throughout ecosystems. When researchers observed sites before and after the outbreaks of the fungus, “pretty much everything we measured changed,” Karen Lips, an ecologist at the University of Maryland (UMD), College Park, told attendees. In addition to their role in ecosystems, amphibians also help humans by controlling insect populations—including the mosquitoes that spread diseases like Zika and dengue fever.
Bsal doesn’t infect all amphibians, just salamanders, but the United States still has a lot to lose. “We have the world’s greatest biodiversity of salamanders,” Vredenburg says. “And currently Bsal is not here as far as we can tell.” Thanks to screening efforts, we already know which U.S. salamanders are vulnerable to Bsal, and the list includes some of the country’s most widespread species. So if the disease were to enter the United States, it could potentially spread through wild populations across the country.
Why is a ban the best solution?
Both Bsal and Bd can stick around in the environment even when they don’t have hosts. “Once it gets in there, we can’t get it out,” Lips says. Even if researchers were to take a whole population of amphibians into the lab and cure them, they could still get reinfected when released back into the wild. So the best way to stop a Bsal outbreak is to keep the fungus from getting to the United States at all. By preventing the entry of salamanders that are known to spread the disease, researchers hope to prevent making the same mistakes they made with Bd. “We missed the boat on Bd,” Lips says.
What happens next?
Not much is known about Bsal in the United States, so the first step is studying U.S. salamanders to see whether the fungus has already made the jump. “We may find out that there are places where it’s already invaded,” Vredenburg says. Other researchers are using the breathing room provided by the ban to learn more about Bsal and Bd, hoping to find some ammunition against the diseases. One strategy is to figure out the environmental weaknesses of the fungi, and identify the areas where amphibians could survive an outbreak. Ana Longo, an ecologist at UMD, is looking at the beneficial bacteria that naturally live on amphibian skin: “This in the future could help us develop probiotics for susceptible species in the same way that probiotics help with our digestion,” she says.